It is well known to provide adjustable lumbar supports in vehicle seats, especially in the seat to be occupied by the vehicle driver. Usually lumbar supports are adjustable to assist in combating driver fatigue by the driver being able to adjust the support to suit his or her individual comfort requirements. Most supports conform to one of two principal types, namely vertically adjustable and horizontally adjustable supports.
The vertically adjustable type of lumbar support has a thin, usually rectangular form provided by a sheet of resilient material or a mesh or grid of resilient elongate members of metal or plastics material. With this type, an actuator is operable to vary the spacing between upper and lower edges of the support to adjust the extent to which the support bows or flexes forwardly about a laterally extending line.
The horizontally adjustable type of lumbar support has the form of a flexible band which extends longitudinally between opposite sides of a vehicle seat frame. An actuator is operable to adjust the depth of rearward curvature of the band, about a vertical line, against pressure applied by an occupant of the seat, such as by adjusting the effective longitudinal length of the band.
With the vertically adjustable type, the forward bowing or flexing causes lower portion of the padding and covering at the front of the seat back to be correspondingly pushed forward, as the support adopts a shape which is complementary to the lumbar region of an occupant of the seat. The arrangement is such that the seat back can have a thickness or depth which is substantially independent of the presence of the lumbar support. Thus, in line with the trend to reduce weight and maximise available space, such as in a land vehicle cabin, a designer's freedom in creating a seat back is not compromised by the need to allow for the thickness of a lumbar support of this type.
In the case of the horizontally adjustable type of lumbar support, a substantially greater thickness needs to be accommodated by the seat back rest. This is because the band has a significant effective depth due to it having a front face which has a convex form conforming somewhat to the lumbar region of standardized occupant. The lumbar support of this type therefore necessitates a thicker seat back rest and therefore limits the extent to which the seat back thickness can be reduced. Thus, it is not possible to reduce the thickness of the seat back rest to much less than the front-to-back thickness of the seat frame and, as will be appreciated, it is the seat back thickness within the frame of a front seat which determines the maximum available space for the knees of a rear seat passenger.
The greater thickness required for horizontally adjustable lumbar supports results from them conforming to the curvature of an occupant's back as a consequence of the designed shape of the flexible band. That is, the flexible band as produced has a front face which is shaped to complement that curvature. Specifically the front face is curved with respect to a horizontal centre line so as to be arcuate in end elevation, whereby as mounted on a seat frame, upper and lower edges of the flexible band are located rearwardly with respect to the centre line. This form of front face is necessary since operation of an actuator to vary the length flexible band acts to vary the curvature of the band somewhat circumferentially with respect to the waist of an occupant, rather than to conform the band to the curvature of the lumbar region.
In essence, the vertically adjustable type of lumbar support is conformable to the curvature of an occupant's lumbar region during adjustment, whereas the horizontally adjustable type has a flexible band which is pre-shaped to conform to that region.
It is an object of the present invention to provide a lumbar support of the horizontally adjustable type which is conformable during adjustment to the curvature of the lumbar region of the occupant of a seat.